Centre diff lock on AWD auto

[idosubaru]

Cut the wire leading to the tranny, splice in a couple of longer lengths, and put a switch in the dash. Now you have selectable AWD to 4wd.

 

that's what i did.

 

The computer most probably won't freak out either

 

mine does no "freaking out", works fine. the only thing that happens out of the ordinary is this....if you leave it "on", in other word the wires disconnected when you start the car (where normally that wire is single strung to the solenoid), the POWER light will flash on the dash. the POWER light flashing indicates the TCU sees a problem. the problem is only in the placement of the switch though - one position completes the circuit and there is no problem, the other position disconnects the circuit which isn't the normal condition of the circuitry so the TCU sees that and flashes the POWER light on the dash. basically the TCU wasn't designed with a switch in mind, so if you have the switch breaking the circuit when you turn the car on it will "think" there's a problem when there is not.

 

it's a 20minute job to put a switch in.

that's about right, easy job. basically most of the time is determining where/how you want to mount the switch, the wiring is easy. cut one wire and install a switch and you're done.

 

i used a 2 pole switch with a light so i can tell when it's "locked".

[idosubaru]

so you DONT know if it will work on the newer cars.

 

wrong again, it will work on the newer cars. all you need is the pin-out number/wire color for your vehicle.

[tunered]

does this put in 50-50 mode?

[nipper]

From another thread .....

 

 

"The connector is just under the hood over the torque converter housing. There are two found in this area -its the one closest to the driver side. It is a 16 contact connector in a 4X4 configuration. To test solenoid C (AWD) electrically, place an ohmmeter between pins 4 and 11 on the connector half going to the transmission. Looking at the contact side of the connector and the locking tab facing up, the pin numbering will start 1 on the upper right corner going left and down. So 4 will be on the upper left corner and 11 will be the third row, second from the left. This should show 9-17 ohms if solenoid windings haven't burned or wire connection hasn't been severed. "

 

 

so know we know where to poke around

 

 

nipper

[idosubaru]

there you go guys. nice work nipper!

 

on a side note....i have resisted mentioning this due to fear needlessly lengthening this thread, but i've been told the older 4EAT's at least can only offer a 60/40 power split, but the drivetrain is "locked" front to back. so you'll still experience the "hopping" and "bucking" of a locked drivetrain/transmission but the technical power split is 60/40 front to back maximum for the 4EAT. don't think it really matters, but i see lots of people mentioning 50/50...which i usually do as well for ease of discussion.

[Andyjo]

gary, from your previous post, it sound to me like you did it? at least the AWD/4WD switch, work well? easy to find the wire harness?

 

oh yeah, and if you throw the FWD fuse in, will the wire read 12v? that'd be an easy find...

[idosubaru]

gary, from your previous post, it sound to me like you did it? at least the AWD/4WD switch, work well? easy to find the wire harness?

 

Yes, i've done it. it's very easy. i did it a year ago or more, so my memory of the exact details is limited.

 

never use the FWD fuse, so i don't know what that does when i insert a fuse.

 

as i said earlier this mod is awesome, one of the best and easiest things you can do to an auto soob. the thing is awesome in snow, mud, offroad.

[idosubaru]

ran across this old message from the guy i mentioned a few posts back who programmed his own TCU for a 4EAT, thought some here might be interested. note the added functionality of controlling line pressure as well:

 

"makes it possible to program line pressue (shift hardness) as a function of TPS (throttle position). It also makes it possible to shift by pushing buttons to manually controll the shift points. I am using a sparco steeringwheel that has two buttons in it, rightbutton to shift up, left button to shift down. It can also control front/rear drive bias. Which means that I can balance the car perfectly to get 4wd drifts through the corners. It has a display to show what gear you are in as well, just like the WRC boys."

[blitz]

"It can also control front/rear drive bias. Which means that I can balance the car perfectly to get 4wd drifts through the corners."

Gary, this part is promting me to mention something that is (or rather IS NOT) at the core of this thread: the basic 4EAT system in question has no center differential, therefore it can't achieve true torque biasing (either fixed or active) and it certainly can't achieve a rear-wheel bias (i.e. 40/60 or 30/70, etc.).

 

Face it folks: it's nothing but a FWD with a friction clutch that allows the rears to be added-in selectively. In my humble judgement, there's nothing sophistocated about it all despite what the sales literature claims. The literature actually states that the system can anticipate slip. Read that again.

[All_talk]

...the basic 4EAT system in question has no center differential, therefore it can't achieve true torque biasing (either fixed or active) and it certainly can't achieve a rear-wheel bias (i.e. 40/60 or 30/70, etc.).

 

Face it folks: it's nothing but a FWD with a friction clutch that allows the rears to be added-in selectively.

This is entirely true.

 

 

In my humble judgement, there's nothing sophistocated about it all despite what the sales literature claims.

I my humble opinion this is not really true… the sophistication is in the programming of the TCU, not the mechanics.

 

 

The literature actually states that the system can anticipate slip. Read that again.

And while this does ring of marketing BS, in some ways it’s true. The TCU uses the TPS to detect aggressive throttle maneuvers which are more likely to produce slip/wheel spin and sets more line pressure to the transfer. In this way the system can anticipate potential slip.

 

Gary

[blitz]

And while this does ring of marketing BS, in some ways it’s true. The TCU uses the TPS to detect aggressive throttle maneuvers which are more likely to produce slip/wheel spin and sets more line pressure to the transfer. In this way the system can anticipate potential slip.

That explains the complete lack of subtlety with which the rear clutch engages AFTER the front wheels begin to slip.

[idosubaru]

i'm well aware of the lack of a center differential and clutch packs/extension housing application for the 4EAT. i guess his description/semantics are a typo as i know he knows as well. wasn't trying to start a technical debate, just mention that he's built his own TCU that also allows control of line pressure for some reason, what ever that offers. he completely tore down the transmission and had all sorts of modifications done to the clutch packs, valve body, etc. his semantics might be off, but his controller allowed manual control of most of the AT parameters...whatever that gives you.

[blitz]

I wasn't being critical of you Gary. I was just kinda amused that the title of the thread is "Centre diff lock on AWD auto" and the premise of the ongoing disscussion has been tending to follow logically.

 

Just making certain it was clear to all that the basic Sube 4EAT AWD has no center diff to lock or bias. Important why? Well dammit, because a simple clutch IS NOT gonna act like a diff - never will.

 

Make way for the bad guy.

[MountainBiker]

You can see how I installed a "ctr diff lock" almost a year ago:

http://www.subaruforester.com/viewtopic.php?t=9268

 

Nothing strange, no idiot lights going on. Works great!

[Storydude1]

You can see how I installed a "ctr diff lock" almost a year ago:

http://www.subaruforester.com/viewtopic.php?t=9268

 

Nothing strange, no idiot lights going on. Works great!

Great minds think alike.

 

See my post a few pages back.

 

[1 Lucky Texan]

maybe somewhat off topic but - is the behavior of the center diff the same in reverse as - say - in first? That is, it is not 'locked' by selection of reverse and waits for slip to be detected before xferring torque?

 

just wondering

[nipper]

its a 50/50 split in low and reverse

 

 

nipper

[NorthWet]

...Just making certain it was clear to all that the basic Sube 4EAT AWD has no center diff to lock or bias. Important why? Well dammit, because a simple clutch IS NOT gonna act like a diff - never will...

Well, I hope that you don't have an LSD... I hear that you need a real differential at the rear.

[blitz]

Well, I hope that you don't have an LSD... I hear that you need a real differential at the rear.

I'll entertain your post, but I'm not sure I'm following what you're saying.

 

SOA currently lists these auto-trans equipped models as using a center differential:

 

Baja Turbo

WRX

STi

Legacy GT Turbo

Outback XT Turbo

Outback 3.0

Tribecca (all)

 

The normally aspirated 4 cyls. (and including Forester XT turbo) don't have a center differential, they're FWD with a rear transfer clutch that repeatedly kicks in & out on snow and mud, courtesy of the day-late-and-dollar-short 'puter algorithym. It makes for squirrely snow handling and it wears on the clutch a lot.

 

FWIW, I brought up the question of adding an override switch about 3 years ago.

[blitz]

http://www.ultimatesubaru.org/forum/showthread.php?p=93600#post93600

 

Alright, I lied ...it was 19 months ago. And it wasn't a question, only a statement.

[cookie]

The only thing I wish I had is low range on my 5 speed but the other day the torquey little 2.5 made up for it sliding though a mud hole. I still would have had more confidence with low range...

I used to take 4 speed overdrives and wire the solenoid to kick the clutches in direct. I did this on a Volvo which gave me an eight speed, a Jag XK140, and a TR3. They all used a similar overdrive system which had clutches controlled by a solenoid. It did cause the clutches to wear a bit early but I was using the heck out of it, especially on the Volvo (P1800 overdrive trans fitted to a 68 122S wagon for those who know Volvos).

I used to use Ford truck two speed switches which mount to the shifter and this is finally the point of the story. This would only give you on and off but man are those two speed switches easy and convenient to use.

like Blitz I think this is a simple system and an on off switch would be neat. It would probably cause premature wear because you would have so much fun using it.

[WoodsWagon]

I think that the simpler you keep it, the better off you will be. You need a switch that has one input and 2 possible outputs, like a switch that you put at the bottom and the top of a set of stairs so that the light can be run from both ends.

 

Input from TCU

l l

switch

l l

tranny / power resistor.

 

I'm not sure if you even need the power resistor if you make sure to always start the car in the AWD position. It depends on the kind of diagnostic checks the TCU runs while it is in operation. The power resistor will fool the computer to thinking that everyting is fine, but needs a good heatsink. The awd system is good enough to start with, so why make your own variable system?

[Andyjo]

The awd system is good enough to start with, so why make your own variable system?

Because i'm a nerd (Engineer). That's about it...

I'm thinking i'll get the 3 pole switch, and just run the 2 other positions (Variable & 4wd) to the same resistor, for now, just incase i get a sudden urge to play w/ the variable split at some later time.

[Gnuman]

That explains the complete lack of subtlety with which the rear clutch engages AFTER the front wheels begin to slip.

 

Blitz, that is actually a failure condition on the 4EAT. It is called "Excessive Slip". Diagnostics are similar to Torque Bind.

[blitz]

Blitz, that is actually a failure condition on the 4EAT. It is called "Excessive Slip". Diagnostics are similar to Torque Bind.

I havt'a say that I'm not surprised to learn that, although I've never had a chance to drive another 4EAT-equipped car in the snow for comparison.

 

I'm not abusive to this thing, and don't baby it either - I pretty much drive it like it was intended to be driven, but at this point I'm comfortable saying that this '02 OBS is a piece of crap. It's been a big dissapointment and IS the reason why I own a second car.